The development of a safe and effective vaccine that protects against human immunodeficiency virus type 1 (HIV-1) infection is a high priority in the attempt to limit the spread f acquired immunodeficiency syndrome (AIDS). Knowledge regarding the requirements for such a vaccine and the efficacy of current vaccine candidates based on the HIV-1 envelope glycoproteins is limited due to the scarcity and expense of chimpanzee animal models. The proposed studies will utilize simian-human immunodeficiency virus (SHIV) chimerae to investigate the requirements for the protection of rhesus macaques from infection by viruses containing the HIV-1 envelope glycoproteins. In the first specific aim, the ability of immunization with the HIV-1 gp120 exterior envelope glycoprotein to confer protection against intravenous challenge with SHIV viruses containing homologous and heterologous envelope glycoproteins will be tested. In the second specific aim, the ability of infection by one strain of SHIV to elicit protection against infection by a second SHV challenge will be investigated. The results of these studies should guide attempts to develop protective immune responses against viruses with the HIV-1 envelope glycoproteins.